Measuring of the coordinates of a subject through a television receiver

ABSTRACT

1. Apparatus for measuring the bearing or elevation of a target displayed on a television screen, comprising a television camera for scanning the area of the target and providing a video signal to a receiver with a cathode ray tube, and, for each bearing or elevation axis, a first saw-tooth generator energised respectively during the synchronisation cycle of the receiver by a synchronising signal, a plurality of selectors comprising triggers successively actuated by a plurality of separate increasing voltages of said saw-tooth signal, a corresponding plurality of slope modifiers each comprising in series an electronic switch and a capacity or a resistance placed in parallel with respect to each other, an integrator R/C incorporating these capacities or resistances and providing a distorted saw-tooth signal, a trip circuit which operates when the voltage of said distorted saw-tooth signal exceeds an adjustable reference voltage and provides a pip signal, a voltmeter measuring said reference voltage, a generator of short pulses of predetermined length energized by said latter trip circuit, and a mixer for adding the video signal and said short pulse and suppling the whole to the T.V. receiver.

United States Narbaits-Jaureguy atet RECEIVER MEASURING OF THECOORDINATES OF A SUBJECT THROUGH A TELEVISION Primary ExaminerMaynard R.Wilbur Assistant Examiner-S. C. Buczinski Att0rneyWatson, Cole, Grindle& Watson EXEMPLARY CLAIM 1. Apparatus for measuring the bearing orelevation of a target displayed on a television screen, comprising atelevision camera for scanning the area of the target and providing avideo signal to a receiver with a cathode ray tube, and, for eachbearing or elevation axis, a first saw-tooth generator energisedrespectively during the synchronisation cycle of the receiver by asynchronising signal, a plurality of selectors comprising triggerssuccessively actuated by a plurality of separate increasing voltages ofsaid saw-tooth signal, a corresponding plurality of slope modifiers eachcomprising in series an electronic switch and a capacity or a resistanceplaced in parallel with respect to each other, an integrator R/Cincorporating these capacities or resistances and providing a distortedsaw-tooth signal, a trip circuit which operates when the voltage of saiddistorted saw-tooth signal exceeds an adjustable reference voltage andprovides a pip signal, a voltmeter measuring said reference voltage, agenerator of short pulses of predetermined length energized by saidlatter trip circuit, and a mixer for adding the video signal and saidshort pulse and suppling the whole to the T.V. receiver.

2 Claims, 6 Drawing Figures [76] Inventor: Jean RaymondNarbaits-Jaureguy,

1, Rue Louis Mercier, Malakoff, France [22] Filed: June 8, 1964 [21]Appl. No.: 373,577

[30] Foreign Application Priority Data June 7, 1963 France 63937296 [52]US. Cl. l78/6.8, 343/5 EM [5]] Int. Cl. H04n 3/00 [58] Field of Search343/5 EM, 5 El; 178/6, 6.8; 235/183, 197; 340/3244 [56] References CitedUNITED STATES PATENTS 2,403,975 7/1946 Graham l78/6.8 2,581,589 l/l952Herbst l78/6.8 2,675,471 4/1954 Berry 235/183 X 2,734,269 2/1956 Clarett 178/6.8 2,938,949 5/1960 Vosburgh... 178/68 2,950,052 8/1960 Knox235/183 X 2,970,187 l/l96l Hinton... 178/6.8 2,057,953 10/1962 Guerth178/6.8 3,076,120 1/1963 Matthew 343/.5 X

ru RECEIVER 3 MEASURING OF THE COORDINATES OF A SUBJECT THROUGH ATELEVISION RECEIVER This invention relates to apparatus for measuring aco-ordinate of a target in an area scanned by a television camera anddisplayed on the screen of a television receiver associated with thecamera.

In modern target detection apparatus it is often required to know aco-ordinate or the co-ordinates of a moving target quickly and with ahigh degree of accuracy.

One method of obtaining such co-ordinates is described and claimed incopending application Ser. No. 341,134 of .lan.29,l964, now abandoned.

In said copending application is described a method of measuring theco-ordinates of a target subject whose image is transmitted bytelevision, by superimposing on the target area viewed the image of agraduated scale by means of an optical system independent from theoptical system of the camera. With such an arrangement the target areaimage and the scale image are transmitted together between the cameraand the receiver and thus any distortion produced by the optical systemand the electrical transmission will influence the displayed picture ofthe target area and the scale image equally. It is well understood thatoptical systems, such as single lenses, do not give an image homotheticto a target, and that T.V. apparatus give a displayed image distorted,for example, by a non-perfect line and frame sweeping in the camera orreceiver, or by the curve of the screen of the latter. Thus by readingthe scale image in the picture a true measure of a targets co-ordinateswill be obtained as both the target image and scale will, if distorted,be distorted to the same extent. The coordinates are usually expressedin terms of elevation and bearing, commonly termed azimuth, and it iswith such co-ordinates that the present invention is primarilyconcerned.

An object of this invention is the provision of improved apparatus formeasuring a co-ordinate of a televised target image.

The present invention includes in its broadest aspect, apparatus formeasuring a co-ordinate of a target displayed on a television receiver,comprising a television camera for scanning the area of the target andproviding a video signal representative of the scanned area, a generatorproviding an electrical non-linear saw-tooth output waveform insynchronism with the scan, a controller providing an adjustableelectrical reference value, a trip circuit connected to receive thereference value and the non-linear saw-tooth waveform and adapted totrip when a predetermined relationship exists between them and initiatean electrical pulse, a mixer connected to mix the pulse with the videooutput from the camera, a television receiver connected to the mixer andfor displaying the video-signal as a picture of the scanned area and thepulse as a marker on the picture, means for adjusting the referencevalue from the controller to move the marker and register it with achosen target in the picture, and an indicator controlled by thereference value and indicating the actual value of the ordinate of thetarget.

Preferably two markers, in the form of mutually perpendicular traces,are provided one for hearing and one for elevation. By adjustingcontrollers the two traces can be registered on a target and itselevation and bearing may then be accurately read from the indicators.

Conveniently the indicators or meters comprise voltmeters calibrated interms of bearing and elevation, respectively, and controlled by thereference values of the controllers expressed as voltages.

The shape of the non-linear saw-tooth is determined, usuallyempirically, in such a way that the output voltage from the trip circuitis proportional to a co-ordinate of the position of the marker on thereceiver and thus of a target with which the marker is registered,independently of the position of the marker on the receiver screen.

The invention is particularly suited with television apparatus employingoptical markers as is described in our copending application Ser. No.341,134. However the invention is equally suitable for use with otherapparatus not employing optical markers.

The invention will now be described in more detail, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram of apparatus for determining the elevation andbearing of a target sighted by a television camera;

FIG. 2 shows theoretical curves of voltage against time; and

FIG. 3 shows practical curves of voltage against time.

FIG. 4 is a graphic illustration of the waveforms produced through oneof the bearing or elevation networks;

FIG. 5 illustrates an example of a pip delivering electronic device; and

FIG. 6 illustrates an example of slope modifiers and distortedintegrator.

The apparatus of FIG. 1 is adapted to give orthogonal co-ordinates ofbearing and elevation by similar circuitry and, for simplicity, only thecircuitry for giving bearing will be described in detail. This circuitryis denoted by the reference numerals 5 to 21. The correspondingcircuitry for giving elevation is denoted by similar reference numeralsin the hundred series, and thus is denoted by the reference numerals to121. It is to be understood that elements 105 to 1211 correspondrespectively to elements 5 to 21.

The apparatus comprises a television camera 1 for viewing the targetarea and providing an output composed of a video signal and line andframe synchronizing signals. The video signal is fed to a mixer 3 whereit is mixed with electrical marker signals from both the bearing andelevation circuitry. The signals from the mixer 3 are applied to atelevision receiver 4 which displays the target area and also twomutually perpendicular traces which are produced by the electricalmarker signals.

The two traces correspond respectively to bearing and elevation and eachis movable parallel to itself by adjustment of the circuitry producingthe trace. thus by aligning the traces with a target its bearing andelevatinon may be read off meters as is described below.

The line and frame synchronizing signals in the output from the camera 1are picked up by a separator 2 which applies one signal to the bearingcircuitry composed of the elements 5 21 and the other signal to theelevation circuitry composed of the elements 105 121.

Considering only the bearing circuitry 5 21, the line synchronizingsignals from the separator 2 are fed to a saw-tooth line generator 5 andto a trigger circuit 6 which initiates operation of an integrator 7.

Considering only the bearing circuitry -21 in FIGS. 1 and 4, the linesynchronising signals from the separator 2 are fed to a line saw-toothgenerator 5, well known in the art, comprising a trigger providing aconstant voltage to a resistance-capacity circuit providing a saw-toothsignal, which initiates operation of another integrator 7 making itpossible to produce a modified sawtooth wave, suitably modified as willbe seen below. This integrator 7, well known in the art, is similar tothe saw-tooth generator 5, and comprises an input receiving a constantvoltage and a circuit with a resistance and a capacity, giving at theterminals an output in sawtooth shape.

The practically linear saw-tooth signal produced by the generator 5 isused to modify the slope of the output signal from integrator 7 throughslope-modifiers 811, each of which operates for a period determined byselectors 12l5 which are themselves actuated by the saw-tooth outputfrom the generator 5.

In order to do so, each of the selectors 12-15 comprises a generator ofpip signals, known in the art and shown in FIG. 5. It consists of atriode the grid of which is set at a cut-off voltage and becomesconductive when the saw-tooth signal applied as an input becomes highenough above the cut-off limit. The triode then delivers a pip signalwhich controls a known bistable trigger 12-15 setting up a constanttension signal during a preselected delay or until the following pip isissued. Said delays following each other for example as four equaldurations t,, t t during the T.V. sweep cycle.

The selectors 12-15 control the slope modifiers which are combined withan integrator 7, as shown in FIG. 6. Each slope modifier is anelectronic switch which introduces successively adjustable capacities CC C and C in the integrator circuit 7. For example, a slope modifier(FIG. 6) consists of a triode which becomes conductive when a signal 12is applied to it, through a capacity which is set up in the R/Cintegrator circuit, the capacity of the circuit being successively C C CC, during the durations t,, t t t,.

The modified saw-tooth from the integrator 7 is applied as a voltage toa trip circuit 16 which operates when the instantaneous value of thesaw-tooth exceeds an adjustable reference voltage. The reference voltageis obtained from a controller 20 having a manually adjustable knob 17for altering the reference voltage. The value of the reference voltageis indicated by a meter 19 calibrated in terms of bearing and thereference voltage is also applied to a line 21 for use elsewhere.

The trip circuit 16 operates to energise a pulse generator 18 whichapplies a pulse of predetermined length to the mixer 3 once for eachline scan. Each pulse produces a black spot or a bright dot on a linedisplayed on the receiver 4 and the position of the spot or dot on theline is determined by the instant of operation of the trip circuit 16which, in turn, is controlled by the controller 20. The bright dots orblack spots on the lines form a trace on the display of the receiver andserves as a bearing index which may be fixed or positionally adjustable.The bearing index, when fixed, may be provided with a scale for enablingdifferent hearings to be read off it. When the bearing index is movableit can be positioned over the target the bearing of which is required,and the bearing read off the meter 19.

The operation of the circuitry 105 121 for determining the elevation ofthe target is similar to that described with reference to the circuitry5 21, and a trace at right angles to the bearing trace is obtained onthe display of the receiver 4 from which the elevation of the target isdeterminable as described above. The elevation index produced by thetrace is obtained by adding to the video signal an appropriately shapedpulse obtained from a pulse generator 1 18, and the elevation may beread directly from the meter 119 which is suitably calibrated.

The operation and purpose of the slope modifiers 8, 9, 10 and 11 of FIG.1 will best be understood from FIG. 2 which shows two plots of voltageagainst time. The curve 21, shown in chain line, is one linear sawtoothin the output of the saw-tooth generator 5. The end-portion andbeginning-portion of the preceding and following saw-teeth,respectively, are also shown in front of and after the curve 21. Theperiod of the sawtooth is equal to one line synchronization.

Theoretically, if it is assumed that no distortion occurs in the signaltransmission between the camera and the receiver, the position of thebearing trace is solely dependent on the instant of operation of thepulse generator 18. This instant is dependent on the saw-tooth appliedto the trip circuit 16 and, if a linear sawtooth is applied as shown at21 in FIG. 2, the instant will be directly proportional to the referencevoltage of the controller 20 as the rate of growth of the linear voltagecurve 21 is directly proportional to time.

Unfortunately, distortions do occur at the optical image in the cameraand in the signal transmission, and the bearing, signified by theposition of the bearing trace, does not vary linearly with thevoltage/time curve 21 in consequence. Thus, if the trip circuit 15should be tripped by a linear saw-tooth voltage, the true bearing willnot be signified by the voltage at which tripping occurs. As a resultthe reference voltage from the controller 20 will not vary linearly asthe bearing alters and the bearing as read from the meter 19 will beinaccurate.

The function of the slope modifiers 8, 9, 10 and 11 is to provide thetrip circuit 16 with a saw-tooth voltage which is not linear but is soshaped that the voltage read by the meter 19 is representative of thetrue bearing signified by the position of the bearing trace on thedisplay of the television receiver 4.

Theoretically the non-linear saw-tooth curve applied to the trip circuit16 is of the shape shown by the full line curve 22 in FIG. 2. From thiscurve it will be seen that a true bearing, represented by a time T, isdenoted by a voltage W read from the meter 19 instead of a voltage V aswould be the case were the linear saw-tooth curve 21 used. Thedifference in voltage between W and V is representative of thedistortion produced during signal transmission and which must becompensated for, if the meter 19 is to give true bearings.

In practice curve 22 would be hard to produce and it is convenient torepresent the curve as a series of chords, shown at 23 in FIG. 3, whichcan be obtained by simple electronic circuitry. The curve 23 correspondsclosely to curve 22 (shown in broken line in FIG. 3) so that only verysmall errors are introduced by this approximation.

The curve 23 is produced as previously explained. Each linesynchronizing pulse from the separator 2 is used to generate a set ofregularly spaced impulses during each saw-tooth cycle. The impulses maybe also produced by suitable means (not shown) such as multivibrator ora suitable delay line circuit. The impulses are integrated in theintegrator 7 which comprises a resistance/capacitance integratingcircuit into which different resistors from the slope modifiers 8, 9, l0and 11 are individually insertable. The resistors are separatelyadjustable and are inserted into the integrator 7 by the selectors 12,13, 14 and 15 respectively. Only one selector can operate at a timebetween successive impulses so that each time a fresh resistor isinserted into the integrator 7 the slope of the saw-tooth outputwaveform is changed.

The impulses integrated at 7 each give rise to an exponential voltagecurve and only the initial part of each curve is used as here the curveis approximately linear and the gradient corresponds to (I/RC). Theselectors 12, 13, 14 and 15 are operated by respective triggers on asort of step-by-step counter previously described fed by the impulses,so that at predetermined instants in the saw-tooth cycle the gradient ofthe modified s'awtooth output from the integrator 7 changes as shown bythe chords 23 in FIG. 3.

The apparatus described enables the bearing to be read directly from themeter 19, which suitably is a voltmeter, and to appear as asubstantially vertical line on the receiver display.

If it is required to calibrate the apparatus the readings of meter 19may be compared with known bearings and these may be obtained fromoptical markers by the method described in my co-pending US. Pat,application Ser. No. 341,134. Periodic checks should be made to ensurethe meter readings of bearing and elevation are correct, and, if errordoes occur, it may be reduced empirically by adjusting the values of thecapacitances or resistors introduced into the integrator 7 so that thecurve 23 is modified further.

The voltages proportional to bearing and elevation obtained from thepoints 21 and 121 may be transmitted to remote stations such asremotely-controlled satellite monitoring sets.

It is to be understood that although the apparatus described refers tovoltages such as would be used with electronic valve components, theapparatus may equally well be transistorised and in this case thereferences to voltages should be replaced by references to intensities.

I claim:

1. Apparatus for measuring the bearing or elevation of a targetdisplayed on a television screen, comprising a television camera forscanning the area of the target and providing a video signal to areceiver with a cathode ray tube, and, for each bearing or elevationaxis, a first saw-tooth generator energised respectively during thesynchronisation cycle of the receiver by a synchro nising signal, aplurality of selectors comprising triggers successively actuated by aplurality of separate increasing voltages of said saw-tooth signal, acorresponding plurality of slope modifiers each comprising in series anelectronic switch and a capacity or a resistance placed in parallel withrespect to each other, an integrator R/C incorporating these capacitiesor resistances and providing a distorted saw-tooth signal, a tripcircuit which operates when the voltage of said distorted saw-toothsignal exceeds an adjustable reference voltage and promarker.

1. Apparatus for measuring the bearing or elevation of a targetdisplayed on a television screen, comprising a television camera forscanning the area of the target and providing a video signal to areceiver with a cathode ray tube, and, for each bearing or elevationaxis, a first saw-tooth generator energised respectively during thesynchronisation cycle of the receiver by a synchronising signal, aplurality of selectors comprising triggers successively actuated by aplurality of separate increasing voltages of said saw-tooth signal, acorresponding plurality of slope modifiers each comprising in series anelectronic switch and a capacity or a resistance placed in parallel withrespect to each other, an integrator R/C incorporating these capacitiesor resistances and providing a distorted saw-tooth signal, a tripcircuit which operates when the voltage of said distorted saw-toothsignal exceeds an adjustable reference voltage and provides a pipsignal, a voltmeter measuring said reference voltage, a generator ofshort pulses of predetermined length energized by said latter tripcircuit, and a mixer for adding the video signal and said short pulseand suppling the whole to the T.V. receiver.
 2. Apparatus according toclaim 1, where the voltmeters are graduated respectively in bearing andelevation by comparison with the graduation of an optical marker.